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TJie Pulsometer.


under large head, and the latter under low head. In con-
sequence, simple centrifugal pumps are only employed for pumping
iarge volumes of water under small head, while positive pumps
are more suitable for pumping small volumes under great pressure.

The Pulsometer is a pump in which steam acts directly
on the water without the intervention of a piston. It is naturally
wasteful in working, but is simple and quickly applied on emer-
gency. Referring to Fig. 724, there are two side chambers A A
to receive the water alternately, and an intermediate vessel H,
whose purpose will be explained. EE are suction and GG delivery
valves, B a foot valve, N the delivery chamber, connected to A by
short pipes FF, and Q the rising main or delivery pipe. To start
the pump, the three vessels are filled through the hole c, the
water resthfg on foot valve B. The ball L being compelled to lie
on one or the other seat at jj, steam is admitted at K, and,
entering, say, the right-hand passage, displaces the water through
F, without agitation, until the level falls to the upper edge of the
orifice. Steam then blows through into F with some violence,
and an instantaneous condensation occurs, causing a partial vacuum
in A. The ball being now drawn to the right-hand seat, water
rises into the right chamber ready for the next stroke, steam
enters the left chamber, and the action is continuously repeated.
The vessel H, though practically uncharged with air, serves the
purpose of an air-vessel, assisting the steady flow into N by the
small head of water which it provides; and to prevent the sudden
shock caused by the rush of suction water, air-cocks D D are placed
on the three vessels, and kept open to a very small amount. The
* Grel' valve at p is often applied to economise the steam supply.
It is simply a short hollow piston, which rises and falls on account
of the difference of pressure within and without it, thus closing pipe
K after a portion of the stroke has been completed. (Seep. 966,)

The Hydraulic Press may be looked on as the seventh
simple machine (see p. 480), and is the basis of the transmissive
principle. Fig. 725 represents the press, with pump attached, as
used to compress cotton bales. The pump A draws water from
the tank B, and forces it, under pressure, to the ram cylinder c,
a rapid exhaust being obtained through the relief valve E when
required* Let D  diameter of ram, and d that of the pump,